[1] This first part of the entry occurs in several lexicographic sources. The Synagoge (Lexica Segueriana 249.13 Bachmann), the Lexicon Ambrosianum, (Ambrosianus B12 sup. fol.77r line 9) and Photius, Lexicon eta53 Theodoridis have almost the same entry: ἧδος: ἡ ἡδονὴ [καὶ τὸ in Lexicon Ambrosianum] ὄφελος . It occurs also in Herodian and Choeroboscus. The original source is probably a scholion (scholia vetera) to the Homeric passage (see note 3) ἦδος: ἡδονή. ὠφέλεια. ὄφελος , 'delight: pleasure. Advantage. Benefit'.
[2] Mention of this linguistic phenomenon can be found in eta 283 and in other grammatical sources as Herodian, Choeroboscus, and the scholia to Apollonius Rhodius, Argonautica. See e.g. Herodian, De prosodia catholica 3.1537: 'disyllabic neuter words terminating with ος and naturally beginning with a long [syllable] are pronounced with the smooth breathing, … And this way is also [the word] ἦδος , which derives from ἡδονή '. At all events, about the right spelling of this word there is no agreement between different sources. Whereas for example Herodian and Aelius Dionysius agree that when pronounced with rough breathing it means vinegar, Tryphon (quoted in Epimerismi Homerici p.193.28) states that the right spelling of the word is, in any case, with rough breathing. Note that Theodoridis and Bachmann, for the reading of the respective lemma in Photius and the Synagoge, prefer the rough breathing. The form with smooth breathing would be Aeolic, as Herodian the Grammarian says, except that it should have alpha rather than eta. Doric ἇδος is attested in the Etymologicum Magnum and γᾶδος in Hesychius (gamma30) with a gamma representing a digamma. But ἅδος "satiety" with a short alpha seems to be a different word, related to the adverb ἄδην (alpha 463).
[3] Homer, Iliad 18.80.